Lythrum salicaria
WARNING: LOCALLY INVASIVE SPECIES
Common Name: purple loosestrife
Type: Herbaceous perennial
Family: Lythraceae
Native Range: Europe, temperate Asia
Zone: 4 to 9
Height: 2.00 to 4.00 feet
Spread: 2.00 to 4.00 feet
Bloom Time: May to September
Bloom Description: Magenta
Sun: Full sun
Water: Medium to wet
Maintenance: Medium
Suggested Use: Water Plant, Naturalize
Flower: Showy
Purple loosestrife (Lythrum salicaria) is listed as an exotic invasive species to Missouri and the Midwest by the Midwest Invasive Plant Network. It is one of the top twenty plants known to be spreading into native plant areas and crowding out native species. It spreads primarily by self-seeding, but will also spread by rhizomes. It is particularly invasive in wetland areas and is on the World Conservation Union’s list of 100 Worst Invasive Species. It is now listed as a noxious weed in Missouri making it illegal to grow, propagate or sell the plant (or which means it may not be sold and must be controlled on all properties).

Culture

Species plants are classified as noxious weeds in the State of Missouri. They may not be sold in commerce and, if currently growing, must be controlled. In states where they may be grown legally, they should be sited in medium to wet soils in full sun to light shade. Flowering spikes should be deadheaded immediately after bloom to prevent self-seeding. Plants may be sheared to the ground after flowering or if foliage becomes tattered from insect damage. If sheared in mid-summer, new foliage generally will appear in 2 weeks with a possible fall rebloom. Plants are most invasive in wet soils.

Noteworthy Characteristics

Lythrum salicaria, commonly called purple loosestrife, is a clump-forming wetland perennial that is native to Europe and Asia. It is believed to have been first introduced into the U.S. from seed contained in ships’ ballast, and it became established in certain estuaries in the northeastern states by the early 1800s. Although many alien invasive plants have naturalized by escaping gardens, purple loosestrife basically began naturalizing on its own in rural areas. It has gradually spread throughout much of the United States, particularly in marshes, swamps, pond peripheries, ditches and wet meadows. In full flower, a colony of purple loosestrife produces spectacular bloom. The problem is that it is so invasive that it can rapidly colonize wet areas and both choke out native vegetation and destroy wildlife habitat. It typically grows 2-4’ tall on stiff upright stems. Downy, stemless, lance-shaped leaves (to 4” long) are opposite or sometimes in whorls of three. Magenta flowers appear in dense terminal spikes (to 18” long) over a long summer to early fall bloom period. A number of cultivars, such as the popular ‘Morden Pink’ have been marketed over the years as sterile plants, but there is evidence that some of these cultivars may interbreed.

Genus name presumably comes from the Greek word lythron meaning blood with reference to the color of the flowers.

Problems

Species plants are very invasive and should not be planted. Japanese beetles may attack the foliage and/or flowers. Susceptible to slugs and snails.

Garden Uses

Notwithstanding serious concerns over invasiveness, these plants grow exceedingly well in bog gardens, along bodies of water or in low spots. They have the potential to prolifically self-seed. If purple loosestrife must be planted in areas where it is legal to do so, sterile cultivars should be used.